1. Field of the Invention
The present invention relates, in general, to methods of diagnosing eye disorders and, more specifically, to methods of diagnosing eye disorders using visual field analysis derived from perimeter field testing.
2. Description of the Art
Visual field testing is used by eye care practitioners to obtain information about the diagnosis and progress of major blindness-causing diseases. For example, field testing is used as a primary tool in diagnosing and monitoring glaucoma.
The normal visual field in an eye extends in varying angular degrees over the eye. Visual sensitivity is greatest in the center of the eye, or at the fovea, and decreases toward the periphery. The field of vision can be represented as a hill or island which, in a normal state, has a generally smooth shape. Field defects characteristic of certain diseases are easily seen as any statistically significant departure from the smooth shape of the normal hill or island of vision. Field defects can be localized, or there may be a general depression of the whole field.
Static or kinetic perimetry testing derived from or based on the well-known Goldmann perimeter is used to determine the variations from normalcy from any individual visual field. In static perimetry testing, the differential light sensitivity at a series of fixed locations in a visual field are determined. Such tests involve a number of selectible patterns, such as central 24, 30 or 60 patterns, peripheral 30/60 patterns, nasal step, temporal crescent and neurological patterns, as well as a central-10, 76 point pattern shown in FIG. 1.
Such static perimeter testing has been automated in the Octopus 201 analyzer sold by Interzeag AG and in the Humphrey Field Analyzer sold by Allegran Humphrey of San Leandro, Calif. Both instruments have pre-settable threshold values for a given visual field which define a normal visual field for a particular individual, taking into account the individual's age, among other factors.
The perimeter data is printed in the form of the visual field pattern, with each point in the visual field being indicated by a specific light sensitivity value, FIG. 2A, a qualitative, symbolic representation indicating a normalcy or defect condition at each stimuli point or a quantitative display using a grey scale representation of the value of each point with respect to a threshold normal value, FIG. 2B. Such measurements provide the practitioner with an indication of the presence of any localized defect or any overall defect in the visual field.
Comparing a series of successive perimeter tests taken over a period of time, FIG. 2C, for the same patient enables the practitioner to determine the progress of a disease. The ability to diagnose the onset of a particular disease or to determine the effects of treatment on a particular eye disease are extremely valuable to the practitioner.
However, the practitioner must compare each test output with preceding and succeeding tests to determine any emerging patterns over the course of numerous tests. Even if the plurality of perimeter test results are printed in a successive arrangement, it is still difficult for the practitioner to easily and quickly detect any emerging patterns without time consuming, careful analysis.
Thus, it would be desirable to provide a method for analyzing visual fields which simplifies the review of such data insofar as enabling the practitioner to easily and quickly determine emerging patterns of disease progress or retraction. It would also be desirable to provide serial visual field test data collected over a number of successive tests on a given patient in a form which is easily understandable.